The present invention relates generally to ceramic tubes and more particularly to a ceramic candle filter and a method of manufacturing the ceramic candle filter.
The hot combustion intake and exhaust gases in industrial and utility cogeneration systems and fossil-based power generation plants entrain a large amount of particulate matter. These hot intake or exhaust gases are typically cleaned prior to venting into the atmosphere, or prior to introduction into a gas turbine for power generation. Dirty gas is directed into filter bags suspended within a chamber, through the filter bags and out the chamber exhaust. For high temperature applications, the filter bags are typically replaced by porous ceramic filters called candles or candle filters. These candle filters are hollow ceramic tubes mounted to a manifold in a chamber downstream form the combustion chamber. The dirty gas within the chamber interior passes through the walls of the candle filter leaving the ash and other particulate matter on the outer collection surface of the candle filter. The clean hot gas then exits through the open top of the candle filters into a turbine or other outlet.
To periodically clean candle filters, reverse pressurization is applied. That is, air at about 200-400 psi is passed back through the candle filter to dislodge the dirt and other particles on the outer collection surfaces of the candle filters for subsequent removal. The dislodged particles fall to a bottom grating from which they are removed from the chamber.
One of the problems with conventional porous ceramic candles is that the ceramic material is relatively brittle. Thus, subjecting the ceramic candles to high pressures during reverse pressurization, can, if any of the candles are at all defective or damaged, cause the candle to break catastrophically during this reverse pressurization. Due to the amount of pressure used, the failed candle literally explodes, sending pieces of the failed candle in all directions. When this occurs, the pieces become projectiles, striking other candles within the chamber and causing a chain reaction of failed candles. This failure occurs very quickly, generally before the operation can reduce pressurization to halt the cascading effects.
One known method of avoiding the breakage problems of ceramic tubes is to use metal tubes instead of ceramic tubes. Two primary disadvantages of metal tubes, however, are their temperature and corrosion limitations. In addition, metal tubes are usually quite heavy and often suffer from fatigue failure. Metals which are more resistant to high temperatures and corrosion are very often too expensive to use for filters.